The present invention concerns a radial piston pump with a pump body, in which a plurality of cylinder borings are provided to receive pump pistons, which are driven by an eccentric cam.
A radial piston pump, as a component of an automatic transmission, has been made known by DE A 41 39 611 and serves for the supply of oil for lubrication as well as for control and activation of equipment. The driving part of the radial piston pump, in this service, is connected with a startup apparatus placed ahead of the transmission, wherein the eccentric cam driving the individual pump pistons, for instance, can be connected with the impeller of a hydrodynamic converter.
The cylinder borings of the radial piston pump are customarily closed, in a radially outward direction, by a valve plug which possesses a centrally located through boring thus forming a pressure passage, wherein all the valve plugs of the radial piston pump are covered by a circumferential band spring. In order to attain a better loading of this band spring by the delivered pump pressure, the plugs, on their upper sides, are provided with parallel striations which terminate within the machined sealing area of the exposed surfaces and the striations are aligned in the circumferential direction of the radial piston pump. In this arrangement, the band spring seals the said centrally located pressure passages as well as the said striations by spring pressure against a collection channel radially located outside of the valve plug. When a radial piston is in the delivery stroke, the band spring is forced free of the sealing surface by means of the pressure in that boring and in the striations which lie in the pressure zone of the radial piston pump.
In the area of the radially, outward directed sides of the pistons, an intake suction port is placed coaxially to the pump axis. This suction port intersects the cylinder boring. Suction intake openings are made by means of this intersection. An annular flow resistance is interposed between the side of the piston and the individual suction port, on each respective piston.
The disadvantage of radial piston pumps of this design is the generation of noise which can extend to an excessive point. These noises arise from the ejection of the oil from the necessary lifting of the band spring. The band spring, when lifted, must push against the pressurized oil standing in the annular collection channel. This burdens the ejection of the oil by the delivering piston and is hence a party to pressure peaks in the cylinder boring which, in the first place, make lifting of the band spring possible.
The purpose of the present invention is to create a radial piston pump with a substantially reduced generation of noise.
The invention also provides, that in each case, an outlet valve is placed in the pressure passages which penetrate the valve plugs, which valve, on its end proximal to the pump piston, is provided with an impact plate.
Advantageously, both ends of the pressure passage are tapered in a conical manner.
The outlet valve further possesses a valve stem, the end of which, proximate to the annular collection channel, is shaped as a cone or a sphere.
A spring embracing the valve stem is between the impact plate and the valve plug and the spring loads the valve stem toward the closed direction.
Because of the fact that the invented radial piston pump has an outlet valve in each valve plug, instead of having a valve band, the advantage is achieved that only a minimal amount of oil is forced into the collection space, by the controlled expulsion of oil from the cylinder borings, so that pressure peaks at the pump pistons in the cylinder borings are substantially reduced. Upon a forward piston thrust in the pumping of oil, a dynamic pressure, which enables an eased opening of the outlet valve, arises on the impact plate. The expelled oil, on this account, is pumped in all directions in the annular collection channel in contrast to the situation in the case of the conventional band spring, wherein the oil could only exit from the sides of the spring.